1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
2. Description of the Related Art
An electrophotographic system image forming apparatus in which a photosensitive member is charged by a corona charger has been known. Particularly, a product using a corona charger called a scorotron provided with a grid to stabilize a charging potential of the photosensitive member has been known. An etching grid in which a mesh area having a plurality of holes in a thin flat plate as a grid is formed by etching has been known. When corona discharge occurs in the air according to the use of the corona charger, discharge products (ozone, nitrogen oxide, and the like) occur. When the discharge products are attached to and laminated on the photosensitive member and are moisture-absorbed under a high-humidity environment, the discharge products cause an image defect called image deletion.
In U.S. Patent Application Publication No. 2010/0158550 A1, an opening portion opposed to a photosensitive drum of a corona charger is covered with a shutter. Specifically, a carriage which supports an end portion of a sheet-shape shutter is moved in an opening longitudinal direction, and an opening of the corona charger is covered at the time of non-image forming to suppress attachment of discharge products to a photosensitive drum.
Since it is possible to efficiently charge the photosensitive member by the corona discharge, a distance between the corona charger and the photosensitive member can be short. For this reason, there are many cases in which the shutter interposed between the corona charger and the photosensitive member has a thin sheet shape. In addition, in order to wind and store the shutter, it is preferable to use a soft material such as a nonwoven fabric obtained by processing a fiber.
However, in the charger provided with the etching grid, when the shutter including the fiber such as the nonwoven fabric obtained by processing a fiber is repeatedly used, the shutter surface becomes rough by contact sliding to longitudinal both end portions of the mesh area in the etching grid adjacent to the shutter, and thus a nap occurs. The nap occurring on the shutter surface drops onto the drum at the time of shutter opening and closing operation.
The nap dropping onto the photosensitive member is conveyed by driving of the photosensitive member, and may be conveyed even to a cleaning unit of the photosensitive member. When the cleaning unit of the photosensitive member is a cleaner blade, the nap is caught at a contact portion of the cleaner blade and the photosensitive member, and a cleaning defect occurs based on the caught nap.